When 1 dice is rolled the total outcome is 6.
And it is given that 3 die are rolled then the total outcomes will be 6 x 6 x 6= 216
Also, the rolled dice must have 1 on red, 2 on blue, and 3 on the reen.
So the favorable outcome is 1 and it will be (1,2,3) on red blue and green dice.
The formula for probability is
Hence, the probability will be 1/216.